Using NASA's James Webb Space Telescope, astronomers have discovered that a brown dwarf (an object that is more massive than Jupiter but smaller than a star) may show auroras, just like the familiar Northern Lights. This is an unexpected mystery because this brown dwarf, known as W1935, is an isolated celestial body in space with no nearby stars to produce auroras.
This artist's concept art depicts the brown dwarf star W47 light years from Earth in 1935. Astronomers used NASA's James Webb Space Telescope to discover methane infrared radiation from W1935. This was an unexpected discovery, as the brown dwarf was very cold and lacked a host star; As a result, there is no significant energy** to heat its upper atmosphere, making methane glow. The team speculated that the emission of methane may be due to the process that produces the aurora, which is shown here in red. **Edited by NASA, ESA, CSA, Leah Hustak (STSCI).
Auroras on Earth are produced when energetic particles from the sun are captured by our planet's magnetic field. These particles fall layer by layer into the atmosphere near the Earth's poles, colliding with gas molecules, forming an eerie, dancing curtain of light. Since no star in W1935 produces stellar winds, external interactions with interstellar plasma or nearby active satellites such as Jupiter's Io may help explain the observed infrared radiation.
Astronomers used NASA's James Webb Space Telescope to study 12 cold brown dwarfs. Two of them – W1935 and W2220 – seem to approximate twins in composition, brightness, and temperature. However, W1935 shows methane emission rather than the absorption profile expected by W2220. The team speculated that the methane emission may be due to the process that produced the aurora. Source**: NASA, ESA, CSA, Leah Hustak (STSCI).
Astronomers using NASA's James Webb Space Telescope have discovered that a brown dwarf star (a celestial body that is more massive than Jupiter but smaller than a star) has infrared emitted by methane, possibly due to energy in its upper atmosphere. This was an unexpected discovery, as the brown dwarf, named W1935, was very cold and lacked a host star; As a result, its upper atmosphere has no significant energy**. The team speculated that the methane emission may be due to the process that produced the aurora.
The findings will be presented at the 243rd meeting of the American Astronomical Society in New Orleans.
To help solve the mystery of methane infrared radiation, the team turned to the solar system. Methane emission is a common feature of gas giants such as Jupiter and Saturn. The heating of the upper atmosphere, which produces this radiation, is associated with the aurora.
On Earth, aurora is produced when high-energy particles blown into space by the sun are captured by the Earth's magnetic field. They enter the atmosphere along the magnetic field lines near the Earth's poles and collide with gas molecules, creating an eerie dancing light curtain. Jupiter and Saturn also have similar aurora processes, including interactions with the solar wind, but they also get their aurora from nearby active moons, such as Europa (Jupiter) and Enceladus (Saturn).
For an isolated brown dwarf like W1935, it is a mystery that no stellar wind contributes to the auroral process and cannot explain the additional energy required for methane emissions in the upper atmosphere. The team speculated that either unexplained internal processes like atmospheric phenomena like Jupiter and Saturn, or external interactions with interstellar plasma or nearby active moons, could help explain methane emissions.
The discovery of the aurora is like a detective story. A team led by Jackie Faherty, an astronomer at the American Museum of Natural History in New York, gained time to survey 12 cold brown dwarfs using the Webb telescope. Among them was W1935 – a celestial object discovered by citizen scientist Dan Caselden, who had been involved in it"Backyard World"(Backyard Worlds Zooniverse); and W2220, an object discovered using NASA's Wide Field Infrared Survey Explorer. The Webb telescope has revealed in fine detail that the W1935 and W2220 are nearly clones in composition. They also have similar brightness, temperature, and spectral signatures of water, ammonia, carbon monoxide, and carbon dioxide. A notable exception is that W1935 exhibits methane emission while W2220 does not exhibit the expected absorption signature. This is seen on a unique infrared wavelength, to which Weber has a unique sensitivity.
We expect to see methane because it's all over these brown dwarfs. But we're seeing the opposite, methane doesn't absorb light: methane is emitting light. My first thought was, what the hell is going on? Why does this celestial body release methane? "The research team used computer models to deduce the reasons behind methane emissions. Modelling work has shown that the energy distribution of W2220 throughout the atmosphere is as expected, cooling as altitude increases. The results of W1935, on the other hand, were unexpected. The best models tend to favor temperature inversion, where the atmosphere warms as altitude increases.
Ben Burningham, the study's lead modeler and co-author of the University of Hertfordshire in the UK, said:"This phenomenon of temperature inversion is truly puzzling. We've seen this phenomenon on planets with nearby stars, which can heat the stratosphere, but it's crazy to see it on a celestial body with no obvious external heat source. "
In search of clues, the team set their sights on our own backyard – the planets of the solar system. Gas giants can be used as surrogates, reflecting what's going on in the atmosphere of W40 more than 40 light-years away, more than 1935 light years away.
The team realized that the phenomenon of temperature inversion is very prominent in planets such as Jupiter and Saturn. Efforts are still being made to understand why they heat up in the stratosphere, but the main theory of the solar system involves the external heating of the aurora and the internal energy transfer from the depths of the atmosphere (the former being the main explanation).
This is not the first time that auroras have been used to explain brown dwarf observations. Astronomers have detected radio radiation from several warmer brown dwarfs and cite aurora as the most likely explanation. Ground-based telescopes such as the Keck Observatory have searched for the infrared signatures of these radio-emitting brown dwarfs to further characterize the phenomenon, but have not reached a conclusion.
W1935 is the first auroral candidate object outside the solar system with methane emission characteristics. It is also the coldest candidate for auroras outside the solar system, with an effective temperature of about 400 degrees Fahrenheit (200 degrees Celsius), about 600 degrees Fahrenheit above Jupiter.
In the solar system, the solar wind is a major contributor to the auroral process, with active moons such as Europa and Enceladus playing a role on planets such as Jupiter and Saturn, respectively. The star W1935 has no companion stars at all, so it is unlikely that stellar winds can contribute to this phenomenon. As for whether an active satellite will play a role in methane emissions on W1935, it is not yet known.
Faherty noted:"With W1935, we now have a spectacular extension of a solar system phenomenon without any stellar irradiation to help explain it. "She added:"With the Webb telescope, we can be really'Open'Chemical reactions'Hood'to see how similar or different the auroral processes are outside the solar system. "
Compilation**: scitechdaily